Use AEBS as internet but show the wireless hard drive (TC) on the network

[MythicFrost]

I currently have a AEBS set up as our router, how can I show the wireless hard drive from our old TC on the network, so that it can be used for backup and for transferring files but without being connected to it on the network?

I thought about extending the network with it, but I fear it will severely slow the network down if it's even compatible with the new AEBS.

Any idea's?